PRELIMINARY ANALYSIS OF STABLE OXYGEN AND CARBON ISOTOPES IN ALLOSAURUS FRAGILIS TEETH AND INSIGHT INTO ONTOGENETIC DIETARY NICHE PARTITIONING

Nail Quarry is a multitaxon dinosaur bonebed from the Upper Jurassic Morrison Formation deposits at Como Bluff, Wyoming. Fossils from the quarry commonly include both shed teeth attributed to Allosaurus fragilis and feeding traces on various theropod and sauropod specimens. Shed teeth and feeding traces vary considerably in size, suggesting multiple individuals of A. fragilis of various ontogenetic stages were feeding at the site. To test this hypothesis, an analysis of stable oxygen and carbon isotopes (δ¹⁸O, δ¹³C) were performed on the carbonate derived from the tooth enamel of five (n=5) Allosaurus fragilis teeth from Nail Quarry. Shed and rooted teeth were selected based on the crown height, basal length and width, and denticle count per centimeter. Preliminary results indicate that the two groups had similar δ¹⁸O and δ¹³C values (δ¹³C: -9.10‰ to -7.25‰; δ¹⁸O: -10.95‰ to -9.93‰ ) despite variation in ontogenetic status. While the current data are limited, these results suggest that the oxygen and carbon composing tooth enamel may have likely been derived from similar source, supporting the hypothesis that ontogenetic niche portioning in Allosaurus fragilis may have been limited. Based on these results, a more robust study sample size may provide more insight into the behavior and ecological role of Allosaurus fragilis throughout ontogeny.